Process for producing high yields of low freeze point jet fuel

ABSTRACT

PROCESS FOR OBTAINING A HIGH YIELD OF LOW FREEZE POINT JET FUEL FROM A HYDROCARBON FEEDSTOCK CONTAINNG MATERIALS BOILING ABOVE THE JET FUEL BOILING RANGE AND CONTAINING AT LEAST 5 VOLUME PERCENT NORMAL PARAFFINS WHICH COMPRISES SUBJECTING SAID FEEDSTOCK TO HYDROCRACKNG AND ISOMERIZATION IN THE PRESENCE OF HYDROGEN AND A CATALYST COMPRISING ALUMINA, A HALOGEN AND A COMPONENT SELECTED FROM THE METALS PLATINUM, PALLADUM AND IRIDIUM AND COMPOUNDS OF SAID METALS, WHEREBY THE AMOUNT OF JET FUEL BOILING RANGE MATERIALS, IS INCREASED AND NORMAL PARAFFINS ARE ISOMERIZED, AND SELECTIVELY HYDROCRACKING THE REMAINING NORMAL PARAFFINS IN THE PRESENCE OF HYDROGEN AND A CATALYST COMPRISING MORDENITE IN HYDROGEN FROM AND AT LEAST ONE HYDROGENATING COMPONENT.

Dec. 28, 1971 C. J. ESAN 3,6311@ PROCESS FOR PRODUCING HIGH YIELDS OF LOW FREEZE POINT JETv FUEL Filed Sept. 9, 1969 DEwAxlNG ZONE 450 -eoo F United States Patent O 3,630,885 PROCESS FOR PRODUCING HIGH YIELDS OF LOW FREEZE POINT JET FUEL Clark J. Egan, Piedmont, Calif., assignor to Chevron Research Company, San Francisco, Calif. Filed Sept. 9, 1969, Ser. No. 856,304 Int. Cl. B011? 11/08; C10g 13/02, 37/02 U.S. Cl. 208-59 10 Claims ABSTRACT OF THE DISCLOSURE Process for obtaining a high yield of low freeze point jet fuel from a hydrocarbon feedstock containing materials boiling above the jet fuel boiling range and containing yat least 5 volume percent normal parans which comprises `subjecting said feedstock to hydrocracking and isomerization in the presence of hydrogen and a catalyst comprising alumina, a halogen and a component selected from the metals platinum, palladium and iridium and compounds of said metals, whereby the amount of jet fuel boiling range materials is increased and normal paraffns `are isomerized, 4and selectively hydrocracking the remaining normal parans in the presence of hydrogen and a catalyst comprising mordenite in hydrogen form and at least one hydrogenating component.

This invention relates to jet fuel production, and more particularly to production of high yields of low freeze point jet fuel from hydrocarbon feedstocks containing materials boiling above the jet fuel boiling range.

PRIOR ART The necessity for jet fuels to be characterized by low freeze points is well known, 'and is reflected in :all military and commercial jet fuel specifications. Many patents have been issued directed to various processes for producing low freeze point jet fuels, for example U.S. Patent 3,110,- 662. Said patent also indicates that it is known to hydrocnack hydrocarbon feed-stocks containing materials boiling above the jet fuel boiling range, to produce jet fuels.

Catalytic dewaxing yof hydrocarbon oils is well known in the art and refers to the reduction of the normal paraffin content of the oils by catalytic conversion of normal parans rather than by mere physical removal of normal paraflins without conversion thereof.

`Copending Egan U.S. patent application Ser. No. 771,- 880 now U.S. Patent 3,539,495 adequately discusses the reasons for catalytic dewaxing of hydrocarbon oils, including reasons why continuing eiforts are being made in the petroleum industry to nd improved dewaxing catalysts and processes.

A recent development in the area `of catalytic dewaxing is provided by accomplishing catalytic dewaxing with a catalyst comprising a crystalline aluminosilicate zeolite in hydrogen form having uniform pore openings with a minor pore diameter as determined by crystallography of not less than 5.8 and a major pore diameter less than 8 angstroms lat a temperature of 4at least 450 F., as disclosed in Texaco Development Corporation South Africa Patent `67/3685, equivalent to U.S. Patent 3,539,458 issued Nov. 10, 1970. The zeolite having the required characteristics is a mordenite-type zeolite. It is highly preferable that the mordenite be in hydrogen form; the sodium form, for example, produces inferior dewaxing results. A catalytic material, suitably a Group VIII metal, preferably a platinum group metal, preferably is associated with the zeolite. The decationized mordenite-type zeolite structures have pore sizes sufficiently large to admit not only the straight-chain hydrocarbons which it is desired to selectively convert to lower molecular weight materials, but also cyclic hydrocarbons; in contrast, the straight-chain hydrocarbons alone are selectively admitted to 5angstrom molecular sieves, the pores of which quickly become saturated with waxy components, causing catalyst deactivation. Accordingly, the decationized mordenite zeolite structures have a greater capacity for sustained selective conversion of straight-chain components than `do S-angstrom molecular sieves. The mordenite-type zeolite has a chain-type zeolite structure in which a number of chains are linked together into a structural pattern with parallel sorption channels similar to a bundle of parallel tubes, in contrast with the three-dimensional structural lattices which arel characteristic of molecular sieve zeolites such as Y-type faujasites. The mordenite-type zeolite dewaxing catalyst preferably comprises a Group VIII hydrogenating component, particularly nickel, platinum, palladium and rhodium, in an amount of 0.1 to l0 weight percent, calculated as metal. When the hydrogenating component is platinum or palladium, the recommended amount is 0.1 to 5.0 Weight percent, preferably 0.5 to 2.5 weight percent. When the hydrogenating component is nickel, cobalt or iron, the recommended amount is 1 to 10 weight percent, preferably 1 to 5 weight percent. Hydrogen, in conjunction with the hydrogenating component of the catalyst, extends the life of the catalyst during catalytic dewaxing by preventing fouling of the pore openings of the catalyst. The catalyst may be preconditioned in hydrogen before use, at a temperature in the range 450 to 1U00 F.

A mordenite-type zeolite in hydrogen form that is suitable for purposes of the process of said South Africa Patent 67/ 3685 and for purposes 0f the present invention is the calclined synthetic Zeolon H mordenite sold commercially by the Norton Company.

As used hereinafter, the terms mordenite, hydrogen mordenite, and mordenite in hydrogen form are intended to include those mordenite-type zeolites indicated by said South Africa Patent 67/ 3685 to be desirable as catalytic dewaxing catalysts or as components of catalytic dewaxing catalysts.

OBJECTS DRAWING The above and additional objects of the present invention, and the ways in which these objects are achieved, will better be understood from the following description when read in connection with the accompanying drawing, which is a diagrammatic illustration of apparatus and ilow paths suitable for carrying out certain embodiments of the invention.

STATEMENT OF INVENITION In accordance with the present invention there is provided a process for producing a jet fuel which comprises contacting a hydrocarbon feedstock boiling in the range 450 to 750 F. and containing at least 5 Weight percent, preferably 5 to 40 weight percent, more preferably at least l0 weight percent, and still more preferably 10 to 30 weight percent, normal parafns in a first reaction zone with hydrogen and a hydrocracking-isomerization catalyst comprising alumina, a halogen, and a component selected from the metals platinum, palladium and iridium and compounds of said metals, at hydrocracking-isomerization conditions including a temperature in the range 700 to 900 P., preferably 750 to 850 F., a pressure in the range of 500 to 3000 p.s.i.g., preferably 1000 to 2500 p.s.i.g., a liquid hourly space velocity in the range 0.1 to l volumes of said feedstock per volume of catalyst per hour, and a total hydrogen rate of 200 to 20,000 s.c.f., preferably 2000 to 8000 s.c.f., of hydrogen per barrel of said feedstock, and at a per-pass cracking conversion of said feedstock not more than 30 weight percent, preferably to 30 weight pecent, to products boiling below the initial point of said feedstock, with accompanying isomerization of normal parains to isoparaffins, and catalytically dewaxing at least a portion of the effluent from said first reaction zone in a second reaction zone by contacting said portion with hydrogen and a dewaxing catalyst comprising mordenite in hydrogen form and at least one hydrogenating component, at catalytic dewaxing conditions including a temperature in the range 400 to 900 F., preferably 550 to 750 F., a pressure in the range of 100 to 2500 p.s.i.g., preferably 400 to 2000 p.s.i.g., a liquid hourly space velocity of 0.2 to volumes of said feedstock per volume of catalyst per hour, and a total hydrogen rate of 200 to 20,000 s.c.f., preferably 2000 to 8000 s.c.f., of hydrogen per barrel of said feedstock, to produce a deWaXed product.

In a preferred embodiment said portion of the effluent from said rst reaction zone that is dewaxed in said second reaction zone boils in the range 450 to 75 0 F., more preferably 450 to 600 F., contains less than 50 parts per million organic nitrogen, preferably less than 5 parts per million organic nitrogen and less than 100 parts per million organic sulfur, preferably less than 50 parts per million organic sulfur, and contains a substantially smaller weight percentage of normal parains than is contained in the portion of the hydrocarbon feedstock having the same boiling range. Despite certain language tending to teach to the contrary in said South Africa Patent 67/ 3685, better results are obtained if the nitrogen and sulfur contents of the hydrocarbon feed to the second reaction zone are kept within the above limits.

In accordance with a further embodiment of the process of the present invention a fraction boiling below 450 F. is removed from the efiluent from said first reaction zone and the portion of the effluent from said first reaction zone that is catalytically dewaXed in said second reaction zone boils above 450 F., preferably in the range 450 to 600 F. The portion of the efiluent from said first reaction zone that boils above 600 F. may be recycled to said first reaction zone.

In a further embodiment of the process of the present invention said first reaction zone and said second reaction zone are located in a single reactor pressure shell, and said hydrocarbon feedstock contains less than l0 parts per million organic nitrogen and less than 50 parts per million organic sulfur. When said rst reaction zone and said second reaction are not located in a single reactor pressure shell, the feedstock supplied to the first reaction zone may contain more than 10 parts per million organic nitrogen and more than 50 parts per million organic sulfur, and the etiluent from said first reaction zone may be hydrofined to reduce the organic nitrogen content thereof to less than 10 parts per million and the organic sulfur content thereof to less than 50 parts per million, prior to supplying the hydroned material to said second reaction zone.

The halogen contained in said catalyst in said first reaction zone preferably is present as combined halogen, that is, in combination with at least one other component of the catalyst. The halogen preferably is selected from fluorine and chlorine, and therefore preferably is present as a halide selected from uorides and chlorides. For example, fluorine may be combined with the alumina component of the catalyst to form aluminum fluoride. The halogen may be present in an amount of 0.01 to 5.0 weight percent, calculated as halogen and based on the total catalyst.

The catalyst in the first reaction zone and the catalyst in the second reaction zone each advantageously may contain rhenium or a compound of rhenium, in an amount of 0.2 to 1.5 weight percent, calculated as metal and based on the total catalyst.

Each component selected from the metals platinum, palladium, iridium and compounds of said metals, that is present in the catalyst in the first reaction zone may be present in an amount of 0.2 to 1.5 Weight percent, calculated as metal and based on the total catalyst.

The deWaXing catalyst in the second reaction zone, which comprises mordenite and at least one hydrogenating component, desirably will contain a Group VIII metal or metal compound hydrogenating component, preferably selected from the metal platinum, palladium, iridium, ruthenium, rhodium and nickel and compounds of said metals. Said dewaxing catalyst advantageously further may comprise carbon in an amount of at least 0.5 Weight percent, based on the total catalyst. The carbon content of the catalyst may be obtained by contacting the catalyst with hydrogen and a heavy hydrocarbon distillate boiling in the range 500 to ll00 F., at a temperature in the range 400 to 900 F., a pressure in the range 5 00 to 3500 p.s.i.g., and a liquid hourly space velocity in the range 0.1 to l0, at a total hydrogen rate in the range 200 to 20,000 s.c.f. of hydrogen per barrel of said distillate, until the catalyst contains the desired amount of carbon. It has been found that the presence of the carbon in the catalyst makes the catalyst more selective for cracking normal parains, and therefore makes the catalyst a more efficient dewaxing catalyst.

The amount of the hydrogenating component present in the catalyst in the second reaction zone is discussed under prior art, above.

DISCUSSION OF DRAWING Referring now to the drawing, there is shown in a diagrammatic illustration of apparatus and flow paths suitable for carrying out the process of one embodiment of the present invention.

A hydrocarbon feedstock boiling in the range 450 to 750 F. and containing at least 5 Weight percent normal paraflins is supplied through line 1 to hydro-crackingisomerization zone 2, which is supplied with hydrogen through line 3. Said feedstock is hydrocracked and isomerized in zone 2 in the presence of a halogen-containing catalyst as previously described and at conditions previously described. The effluent from zone 2 is passed through line 4 to separation zone 5, which may be a distillation zone, and is there separated into fractions, including:

(l) A C( fraction which is withdrawn through line 6;

(2) A 450 F.- fraction which is withdrawn through line 7;

(3) A fraction boiling in the range 450 to 600 F. which is passed through line 8 to dewaxing zone 9;

(4) A 600 to 750 F.- fraction which is recycled from zone 5 to zone 2 through line 10.

The fraction entering zone 9 through line 8 is catalytically deWaXed in zone 9 in the presence of hydrogen entering zone 9 through line 11 and in the presence of the mordenite-containing dewaxing catalyst previously described, at the catalytic deWaXing conditions previously described. The effluent from zone 9, reduced in normal paraffin content compared with the fraction in line 8, is recovered from zone 9 through line 12 for use in part or in its entirety as a superior, low freeze point jet fuel. Said fraction may be further hydrogenated in a conventional manner, if desired, to further improve the smoke point thereof.

The hydrocarbons supplied to zone 9 through line 8 preferably have a limited nitrogen content and sulfur content, as previously described. This limited nitrogen EXAMPLES The following examples will serve to further illustrate the process of the present invention.

Example 1 A hydrocarbon feedstock Was subjected to catalytic isomerization and then to catalytic dewaxing in accordance with the process of the present invention. The hydroisomerization catalyst was in the form of a xed bed located within a reactor pressure shell above a xed bed of the catalytic dewaxing catalyst located within the same reactor pressure shell. Each catalyst was present in an amount of 50 volume percent of the total catalyst in the reactor shell. The hydrocarbon feedstock and hydrogen were introduced into the reactor shell at the top, and a liquid product .was removed from the bottom of the reactor shell. Details of the operation were as follows:

A. Hydrocarbon feedstock:

ASTM D86 distillation:

50% 521 90%/EP 542/560 Gravity, API 33.3 Organic sulfur, p.p.m. 10 Organic nitrogen, p.p.m. 0.29 Freeze point, F. +7 Pour point, F -20 Aniline point, LF. 157 Parafns, vol. percent 24.6 Naphthenes, vol. percent 67.0 Aromatics, vol. percent 8.4 INaphthalenes, vol. percent 0.6 Smoke point, mm. 19/18 Normal paraiiins, wt. percent: 5.2

'.lsomerization Dewaxing catalyst catalyst B. Operating conditions (upper bed) (lower bed) Temperature, F 800 645 Pressure, p.s.i.g. 2,100 2, 100 LHsV, V./V./hr 3. o 3. o Total hydrogen rate, s.c.f. of hydrogen 5, 000 1 5,000

per barrel of hydrocarbon feedstock.

1 Adjusted by eiect of reaction in upper bed.

l 0.37 Weight percent of total catalyst.

2 0.35 Weight percent of total catalyst.

8 Approximately 98.5 Weight percent of total catalyst. 4 0.5 Weight percent o total catalyst, calculated as F.

5 0.22 Weight percent of total catalyst, calculated as Cl. 6 2.0 weight percent of total catalyst.

7 98.0 Weight percent of total catalyst.

D. Product distribution, weight percent:

5 RC4 iC5 1.5

iCG 1.0

10 C7300 1F. 3.5 300 F.i 85.5

Total 100.0

E. Yield of 300 F.-{ product based on hydrocar- 1) bon feed, weight percent 85.5

F. Characteristics of 300 F plus product:

Boiling range, F 300-575 Gravity, API 35.1

Aniline point 154 Smoke point, mm. 18

Freeze point, F. below -94 Example 2 The operation of Example l is repeated, using an additional portion of the same feedstock, at the same conditions except that the temperature in the upper bed is 550 F. rather than 800 F., so that the first bed serves merely to hydrogenate the feedstock rather than to cause hydrocracking and isomerization of any appreciable amount of the normal paraiiins therein.

Because the mordenite catalyst alone does not lower the boiling range of the feed suiliciently to meet jet fuel specifications, only the lower-'boiling 75 volume percent of the 300 F.-iproduct is suitable for blending into jet fuel. The final yield of jet fuel is 0.75 X92 weight percent, or -69 Weight percent, of product having a freeze point of -61 F.

What is claimed is:

1. A process for producing a jet fuel which comprises contacting a hydrocarbon feedstock boiling in the range 450 to 750 F. and containing at least 5 weight percent normal parailins in a iirst reaction Zone with hydrogen and a hydrocracking-isomerization catalyst comprising alumina, a halogen, and a component selected from the metals platinum, palladium and iridum and compounds of said metals, at hydrocracking-isornerization conditions including a temperature in the range 700 to 900 F., a pressure in the range 500 to 3000 p.s.i.g., a liquid hourly space velocity in the range 0.1 to 10 volumes of said feedstock per volume of catalyst per hour, and a total hydrogen rate of 200 to 20,000 s.c.f. of hydrogen per barrel of said feedstock, and at a per-pass cracking conversion of said feedstock not more than 30 Weight percent to products boiling below the initial boiling point of said feedstock, with accompanying isomerization of normal parailns to isoparains, and catalytically dewaxing at least a portion of the effluent from said first reaction zone in a second reaction zone by contacting said portion with hydrogen and a dewaxing catalyst comprising synthetic mordenite in hydrogen form and at least one hydrogenating component, at catalytic dewaxing conditions including a temperature in the range 400 to 900 F., a pressure in the range to 2500 p.s.i.g., a liquid hourly space velocity of 0.2 to 25 volumes of said feedstock per volume of catalyst per hour, and a total hydrogen rate of 200 to 20,000 s.c.f. of hydrogen per barrel of said feedstock, to produce a dewaxed product.

2. A process as in claim 1, wherein said feedstock contains at least 10 Weight percent normal parains.

3. A process as in claim 1, wherein said portion of the effluent from said iirst reaction zone that is deWaXed in said second reaction zone boils in the range 450 to 750 F., contains less than 10 parts per million organic nitrogen and less than 50 parts per million organic sulfur, and

contains a substantially smaller weight percentage of normal parains than are contained in the portion of said hydrocarbon feedstock having the same boiling range.

4. A process as in claim 3, wherein said portion of the efuent from said rst reaction Zone that is dewaxed in said second reaction zone boils in the range 450 to 600 F.

S. A process as in claim 1, wherein said rst reaction zone is operated at a perpass cracking conversion of said feedstock in the range 5 to 30 weight percent of products boiling below the initial boiling point of said feedstock, and wherein a fraction boiling below 450 F. is removed from the effluent from said first reaction zone and wherein said portion of the eluent from said first reaction Zone that is catalytically dewaxed in said second reaction zone boils above 450 F.

6. A process as in claim 1, wherein a portion of the effluent from said rst reaction zone that boils above 600 F. is recycled to said first reaction zone and wherein the portion of the eiuent from said reaction zone that is catalytically dewaxed in said second reaction zone boils in the range 450 to 600 F.

7. A process as in claim 1, wherein said first reaction zone and said second reaction zone are located in a single reactor pressure shell, and wherein said hydrocarbon feed- References Cited UNITED STATES PATENTS 3,127,339 3/1964 Scott 208-112 3,132,087 5/1964 Kelley et al 208-60 3,259,564 7/1966 Kimberlin 208-111 3,395,096 7/1968 Gladrow et al. 208-111 3,438,887 4/1969 Morris 208-87 3,516,925 6/1970 Lawrence et al. 208-111 3,539,498 11/1970 Morris et al. 208-111 DELBERT E. GANTZ, Primary Examiner G. E. SCHMITKONS, Assistant Examiner U.S. Cl. X.R. 208-66, 111, 112 

